How to avoid shrinkage and deformation in PEEK injection molding: Expert tips

Polyetheretherketone (PEEK) is one of the most sought-after high-temperature thermoplastics due to its unique combination of mechanical strength, chemical resistance and high temperature resistance. Due to these characteristics, PEEK is widely used in industries such as aerospace, medical and automotive. However, despite its pros, injection molding PEEK is a technological challenge. One of the key issues when using PEEK material is shrinkage and deformation of parts after the molding process. In this blog, we will look at ways to minimize shrinkage and deformation to ensure high quality finished products.

Shrinkage and deformation: the essence of the problem

Shrinkage and deformation are the two main problems that occur during injection molding of PEEK material. These deficiencies can significantly affect dimensional accuracy and surface quality of the products.
Shrinkage - is the reduction in volume of the material as it cools after casting. Shrinkage can lead to distortion of the part shape, geometry and dimensional deviation.
Deformation occurs when parts of the product cool unevenly, causing internal stresses in the material. This can cause distortion of the shape and reduced accuracy.
To prevent these problems, a number of key factors must be considered throughout the injection molding process.

Main factors affecting shrinkage and deformation of PEEK

1.Melting point
One of the main factors affecting the quality of PEEK injection molding is the melting point. PEEK has a high melting point of about 343°C, and effective processing requires maintaining melting between 360-400°C. If the temperature is not high enough, the material may not fully melt, resulting in under-molding and further deformation of the product. On the other hand, an excessively high temperature may lead to thermal decomposition of the polymer, which will also affect the properties of the final product.

2.Mold temperature
Mold temperature has a significant impact on product shrinkage and deformation. PEEK requires a higher mold temperature than other thermoplastics and the recommended temperature is between 160-200°C. If the mold temperature is not high enough, there will be uneven cooling of the material, which can cause internal stresses and product deformation. Maintaining a stable and uniform mold temperature is key to minimizing the likelihood of defects.

3.Injection pressure
Injection pressure is an important factor in the PEEK injection molding process. Due to the high viscosity of this material, high injection pressures (approx. 1000 to 2000 bar) are required. Low pressures can result in incomplete mold filling, which can lead to dimensional accuracy and shrinkage problems. However, excessive pressure can overload the material and cause cracks and defects.

4.Injection rate
The injection speed must be set correctly to ensure even distribution of material in the mold. If the injection speed is too low, the material may not fill the mold properly, resulting in underfilling and distortion of the product. On the other hand, an excessively high injection rate can cause turbulent material movement, which can lead to air bubbles and surface defects. Optimal injection speed helps prevent uneven cooling and product distortion.

5.Cooling time
The cooling time of PEEK is significantly longer due to its low thermal conductivity, which distinguishes it from other thermoplastics. It is important to adjust the cooling time correctly to prevent deformation. If the cooling process is too fast, the outer layers of the material can become solid while the interior remains in a liquid state. This leads to uneven stress distribution, which in turn leads to deformation and warping of the product. Optimizing the cooling time will help to avoid these problems and ensure stable product dimensions.

Practical tips to prevent shrinkage and warping:

1.Using molds with high quality thermocontrol molds
To reduce shrinkage and warpage, it is important to use molds with an effective thermal control system. The mold temperature should be uniform across the entire mold surface to ensure uniform heat distribution. Molds with an integrated cooling or heating system will ensure uniform cooling of the material, which will help avoid internal stresses. Optimizing the mold structure

2. Optimizing mold design

The structure of the mold is also of significant importance in preventing product deformation. Uniform distribution of material within the mold and minimizing wall thickness variations help reduce the likelihood of warping. The more uniform the geometry of the product, the easier it will be to control the cooling of the product, which will reduce the likelihood of warping.

3.Selection of optimal process parameters
Each production is unique, and process parameters must be customized to the specific product geometry and equipment characteristics. Performing tests and inspections to adjust melting temperature, pressure and cooling time is an important step to optimize the process. Regular monitoring of process performance also helps to maintain consistent product quality.

4.Detailed drying of the material
PEEK tends to absorb moisture, which can adversely affect the injection molding process. Moisture contributes to the formation of pores, undermolding and, as a result, defects and distortions of the product. The material must be thoroughly dried before molding can begin. The recommended temperature for the drying process is approximately 150°C for 3-4 hours. Control of the holding pressure

5.Holding pressure

Holding pressure is the pressure applied after the mold is filled to compensate for shrinkage of the material as it cools. Continuous control of the holding pressure can reduce shrinkage and prevent defects. If sufficient holding pressure is not provided, dimensional stability problems can occur.

Features of working with PEEK: Comparison with other materials.

PEEK offers several advantages over other engineering thermoplastics such as PPS and PEI, but requires more stringent processing control.

–Melting point PEEK is higher than most other materials, which provides increased thermal resistance, but requires more precise temperature control.

–Chemical resistance PEEK outperforms most other plastics, making it ideal for use in corrosive environments. It also requires the use of specialized equipment that is resistant to aggressive substances.

–Mechanical strength The PEEK is higher than many other thermoplastics, making it ideal for high stress applications but requiring more careful control of the cooling process.

PEEK injection molding is a complex process that requires a high degree of skill and the use of specialized equipment. To reduce the risks of shrinkage and deformation, it is necessary to control all stages of the process, from material preparation to the final processing of the product.

By following recommendations for optimizing process parameters, equipment selection and proper mold design, you can significantly reduce the likelihood of defects and ensure high product quality. PEEK is a material with outstanding characteristics, and its proper processing opens up a wide range of applications in high-tech industries.